The present invention relates to an ink jet printer system and, more particularly, to a means and method for refilling an ink jet cartridge which supplies ink to an ink jet printhead.
Ink jet printers, or plotters, of the so-called "drop-on-demand" type have at least one printhead from which droplets of ink are directed towards a recording medium. Within the printhead, the ink is contained in a plurality of channels and energy pulses are applied to transducers to cause the droplets of ink to be expelled, as required, from nozzles at the ends of the channels.
In a thermal ink jet printer, the energy pulses are usually produced by resistors, which are individually addressable by current pulses to heat and vaporize ink in a channel or recess proximate to the nozzle. As a vapor bubble grows, ink bulges from the nozzles until the current pulse has ceased and the bubble begins to collapse. At that stage, the ink within the channel or recess retracts and separates from the bulging ink which forms a droplet moving in a direction away from the nozzles and towards the recording medium. The channel or recess is then re-filled by capillary action, which in turn draws ink from a supply cartridge. Operation of a thermal ink jet printer wherein the ink is expelled from channels is described in, for example, U.S. Pat. Nos. 4,638,337 and 4,774,530, which disclose a printer of the carriage type having a plurality of printheads, each with its own ink supply reservoir, mounted on a reciprocating carriage. The nozzles of each printhead are aligned perpendicular to the line of movement of the carriage and a swath of information is printed on the stationary recording medium as the carriage is moved in one direction. The recording medium is then stepped, perpendicular to the line of carriage movement, by a distance equal to the width of the printed swath and the carriage is then moved in the reverse direction to print another swath of information.
Many current ink jet printers and plotters utilize disposable printhead cartridges which incorporate self-contained ink supplies. However, the current printhead technology has advanced to the point where the lifetime and reliability of the structural components of the printhead, such as the resistive heater elements, far exceed the usage life of the self-contained ink supply. For example, for a Xerox 4004 printhead, the standard ink charge will last for 5.times.10.sup.6 pulses per jet while the heater reliability includes minimum lifetimes in excess of 5.times.10.sup.7 pulses per jet. Thus, it is seen that discarding an ink cartridge supply because it's ink charge has been expended is wasteful and environmentally unfriendly.
The need for refilling ink jet cartridges to exceed lifetime is therefore well recognized and several methods and devices have been presented to accomplish this. One approach is to connect a second auxiliary ink reservoir to a main printhead cartridge to provide a continuous resupply during operation. U.S. Pat. No. 5,369,429 discloses this technique.
Other techniques are directed to removing the ink cartridge from the system and refilling through either an already existing vent hole by means of an ink-filled syringe or by using a special tool to form a new, or enlarge an existing, vent hole. The cartridge is then refilled by means of a tube or syringe from an auxiliary supply. Disclosures of this type of refill are found in U.S. Pat. Nos. 5,199,470 and 5,329,294. U.S. Pat. No. 4,968,998 discloses refill of a cartridge without removing the cartridge from the printhead by moving the printhead to a service station and inserting a refill tube into an aperture in the cartridge body.
The above techniques are not suitable for many types of printheads and printing systems. For example, many cartridges contain the ink in a collapsible bag so penetration of the cartridge with a syringe or refill tube would puncture the bag. Further, some ink cartridges have venting tubes which are either inaccessible or which, once modified, must be restored for the original venting purpose.